Many of the issues involved in sending communication signals over DC power lines are similar to sending such signals over the AC power grid. For example, the properties of the transmission medium can vary greatly. As another example, the amount and nature of noise sources are very difficult to predict.
However, there are some important differences too. While on the AC power grid, loads are mostly of an inductive nature, and some loads may be resistive and a few subtly capacitive. On a DC power bus, virtually all loads and sources are capacitive in nature. Another key difference lies in the use of transformers to convert between different voltage levels on an AC power grid that cannot be similarly employed on a DC bus. Hence, a majority of sources and loads on a DC bus employ electronic DC-DC converters, which are very strong noise emitters.